1. Field of the Invention
The invention relates to a method for setting a knock determination period in an internal combustion engine, a method for setting a fuel injection timing in an internal combustion engine, and a control apparatus for an internal combustion engine.
2. Description of the Related Art
As is well known, in many internal combustion engines a knock determination is made to determine the presence or absence of knock and knock control is performed in which the ignition timing and the like is adjusted in accordance with the determination results. Ordinarily, the knock determination is made using a knock sensor, which is a vibration detecting sensor mounted on the cylinder block or the like. The presence or absence of knock is then detected based on an output signal from the knock sensor during a predetermined period (i.e., a knock determination period) after ignition in each cylinder.
Recently in-cylinder internal combustion engines, which have a fuel injector provided such that the nozzle hole is exposed to the combustion chamber, and in which fuel is injected directly into the cylinder, have been put into practical use. Some in-cylinder internal combustion engines can switch combustion systems, changing between homogeneous combustion and stratified-charged combustion, by changing the fuel injection timing and the like. Other in-cylinder internal combustion engines improve the combustion state within the cylinders by controlling the airflow in each cylinder with an airflow control valve provided in the intake port or the like.
When the combustion mode of the internal combustion engine is changed by switching the combustion system or using airflow control or the like, the rate of combustion inside the cylinder changes which also changes the timing of knock occurrence after the fuel is ignited. In response to this, JP(A) 10-159642 proposes technology which changes the knock determination period according to the combustion mode in an in-cylinder internal combustion engine. This technology enables suitable knock detection to be performed irrespective of a change in the timing of knock occurrence, which occurs when the combustion mode changes.
The fuel injector that injects the fuel in the internal combustion engine is designed such that, to start a fuel injection, an electromagnetic solenoid is energized to drive a nozzle needle away from a valve seat, thus opening a valve. To stop the fuel injection, the electromagnetic solenoid is de-energized such that the nozzle needle comes to be seated back against the valve seat.
When operated, this kind of fuel injector produces vibration, such as of a sound produced by the nozzle needle hitting the valve seat when the valve closes. This vibration produced in accordance with the operation of the fuel injector may ride as noise on the output signal from the knock sensor. In particular, there is a tendency for the effect from the noise produced by operation of the fuel injector (hereinafter referred to as “fuel injector noise”) on the output signal from the knock sensor to be greater with in-cylinder internal combustion engines than with port injection type internal combustion engines due to the fact that in in-cylinder internal combustion engines the fuel injector is mounted nearer the knock sensor.
Conventionally, however, the knock determination period and the fuel injection timing were set without consideration given to the effects from the vibration produced by operation of the fuel injector. Therefore, it is possible that fuel injector noise may ride on the output signal from the knock sensor during the knock determination period, which may result in an erroneous determination that knock is occurring even if, in actuality, it is not.